If arsenic (As) is contained in petroleum fractions such as straight run naphtha, kerosene and fractions formed by catalytic cracking or the like, in producing petrochemical starting materials such as ethylene or petrochemical products such a polymers from the petroleum fraction using a catalyst, the poisoning of the catalyst by arsenic will occur and the catalytic activity will be rapidly reduced or coking will be accelerated in the pyrolysis of the petroleum fractions. Particularly, when noble metals such as Pt and Pd are used as catalysts, the catalysts can be significantly and adversely affected even if arsenic is present in a minor amount. It is highly desired that arsenic is removed from petroleum fractions such as straight run naphtha to a specific amount or below.
Various processes for removing arsenic from a petroleum fraction have been known in the prior art. Such processes include a process wherein a petroleum fraction is subjected to hydrodesulfurization treatment to remove arsenic together with sulfur. According to this process, arsenic is removed together with sulfur. However, when the removal of arsenic is desired, the installation cost and running cost are increased. Further, the process is unsuitable for feed naphtha having a small arsenic content for steam cracker. There have been proposed another process wherein a petroleum fraction is brought into contact with an alkali metal or alkaline earth metal, and a further process wherein a petroleum fraction is brought into contact with a nitrogen containing compound having three substituted moieties and one unpaired electron or a lignite active carbon. However, these processes have such problems that the dearsination ability is low and a large amount of a dearsinating agent is required.
Further, there has been proposed a process wherein arsenic contained in a petroleum fraction is directly oxidized with an oxidizing agent such as an organic peroxide to form heavy products and such heavy products are distilled and separated. However, when highly reactive olefins are contained in the petroleum fraction, these olefins may be polymerized or oxidized to cause troubles.
There has been known a further process wherein arsenic contained in a petroleum fraction is brought into contact with a copper impregnated active carbon to remove arsenic. However, this process has such problems that this copper impregnated active carbon is expensive and the percent removal of arsenic is not always satisfactory.
We have carried out studies in order to overcome such problems and to efficiently remove arsenic from a petroleum fraction. We have now found that, when the petroleum fraction is brought into contact with a specific adsorbent, arsenic can be efficiently removed. The present invention has been completed on the basis of such a discovery.
The present invention is intended to overcome the problems associated with the prior art as described above. An object of the present invention is to provide a process for removing arsenic from a petroleum fraction, wherein arsenic which is a poison for catalyst can be easily and efficiently removed from the petroleum fraction and wherein even if highly reactive olefins are contained in the petroleum fraction these olefins are not polymerized in the course of the removal of arsenic, thus no troubles occur.